Sensors for measuring the viscosity of a fluid are already known from German Patent Application No. 101 12 433.3. When working with sensors of this type, an oscillator is inserted into a fluid, and the oscillation frequency and the damping of the oscillation are observed. The viscosity of the surrounding fluid may be inferred based on a shift of the oscillation frequency and/or an altered damping.
The sensor of the present invention for measuring the viscosity of a fluid has the advantage that the accumulation of dirt on the surface of the oscillator is prevented or markedly reduced by a dirt-repellent coating. The long-term durability of the sensors is thus improved.
Modified, oligomeric polysiloxane coatings or fluorine-containing plastic coatings are considered in particular as dirt-repellent coatings. In this context, the layer thickness is perceptibly less than the penetration of an undulation into the fluid, i.e. less than 1 xcexcm, particularly less than 0.5 xcexcm. The oscillator preferably takes the form of a shear-mode transducer, since this oscillation mode exhibits a particularly strong dependence on the viscosity. Preferably a quartz plate from a so-called simply (singly) rotated section, as, for example, the AT section is used The oscillator is excited to oscillate particularly simply by applied electrodes which are formed as surface metallizations.